Chem 232 Lecture 12 - UIC Department of Chemistry - University of ...
Chem 232 Lecture 12 - UIC Department of Chemistry - University of ... Chem 232 Lecture 12 - UIC Department of Chemistry - University of ...
Regioselectivity - 1st RationaleSteric Effects Control Regioselectivity. . .boron is larger than hydrogen; it prefers to add to the less stericallyhindered side of the double bond, which is the least substituted side.HBH 2CH 3XHBHHCH 3HHBHHCH HH 2 BHCH 3Steric strain in transitionstate raises Eact for thispathway - slower reactionUniversity of IllinoisUICat Chicago CHEM 232, Spring 2010Slide 14Lecture 12: February 1814
Regioselectivity - 2nd RationaleElectronic Effects Control Regioselectivity. . .both carbons in alkene develop partial positive charge in transition state; moresubstituted = more partially positively charged = hydride (H:) transfer preferred(faster) to that carbon atom.Lewis acidLewis baseπ-complexπ-complexmost substituted =most partially positively charged =most electrophilic carbon atom =want electrons from a nucleophile mostrearrangedπ-complexUniversity of IllinoisUICat Chicago CHEM 232, Spring 2010Slide 15Lecture 12: February 1815
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Regioselectivity - 1st RationaleSteric Effects Control Regioselectivity. . .boron is larger than hydrogen; it prefers to add to the less stericallyhindered side <strong>of</strong> the double bond, which is the least substituted side.HBH 2CH 3XHBHHCH 3HHBHHCH HH 2 BHCH 3Steric strain in transitionstate raises Eact for thispathway - slower reaction<strong>University</strong> <strong>of</strong> Illinois<strong>UIC</strong>at Chicago CHEM <strong>232</strong>, Spring 2010Slide 14<strong>Lecture</strong> <strong>12</strong>: February 1814
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